jfriend00 at 23:35 jfriend00 thanks for the comments. Event loop +Web APIs => asynchronous behavior. FYI, the request-promise library supports a timeout option already so if you just want to timeout waiting for a response, you can use the option already built into the request-promise library. One of their main purpose is to provide us a taste of asynchronous execution callback will be added to the Callback Queue when specified time is reached, but, we know, it could already have callbacks in Callback Queue waiting for execution. Its only when I kill my test API server that my client app immediately continues. I can verify that the app is making contact with server. setInterval(callback, time) – runs a callback at a specified time interval My client app (reactJS) hangs once I make a call to the test API endpoint - I expected it to timeout within 2 seconds (my set timeout).setTimeout(callback, time) – runs a callback once after specified amount of time.Let us take as example the following functions: Callback Queue: a queue of event handlers that are waiting to be executed When action is triggered, the corresponding callback function gets added to Callback Queue.The event loop process waits for the Call Stack to be clear before pushing callbacks from the Callback Queue to the Call Stack. Calling timeout.ref() multiple times will have no effect. Returns: Timeout a reference to timeout When called, requests that the Node.js event loop not exit so long as the Timeout is active. What happens when we call setTimeout, http.get or fs.readFile (or any async functions)?Those calls are popped off and sent to the Web API container from the Stack and sit there until an action is triggered (timer reaches its time, http request finishes getting data.).The main thread (Call Stack) continues executing sequentially your script while async functions are waiting on Web API.īrowser has set of web APIs which runs in their own thread or isolated from javascript runtime (setTimeout is part of the web API, other examples will be AJAX/requests or may be a web worker response). If true, the Timeout object will keep the Node.js event loop active. The Call Stack is part of the JS engine (one call stack=>single thread=>one thing is executed at a time). When we invoke a function, in our script,it gets added to something called the Call Stack. The browser contains different libraries which can do things like sending HTTP requests, listen to DOM events, delay execution using setTimeout or setInterval. First, JavaScript is a single-threaded language which means only one statement is executed at a time and that has only one memory heap and one call stack: two bits of script cannot run at the same time.īut how we do with JS to simulate concurrency? we use callback. How it works Timeout (Optional): Enter the number of seconds for which you want to wait for the server to send response headers.
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